Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to the energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor shaft. The rotor shaft may, in turn, be linked to devices such as an electric generator to produce electricity.
To increase efficiency, engines are typically operated near the operational limits of the engine components. For example, to maximize the amount of energy available for conversion into electricity, the products of combustion (also referred to as the working gas or working fluid) often exit the combustion section at high temperature. This elevated temperature generates a large amount of potential energy, but it also places a great deal of stress on the downstream fluid guide components, such as the blades and vanes of the turbine section.
In an effort to help components within the engine withstand these temperatures, a number of strategies have been developed. One strategy is to manufacture these components from advanced materials that can operate in high-temperature environments for extended periods. Another strategy includes protecting the components with special, heat-resistant coatings that lessen the effects of exposure to elevated temperatures. In still another strategy, the components may be cooled through a variety of methods. Each of these strategies has advantages and disadvantages, and the strategies may be combined to fit various situations and operating conditions.
In situations where turbine components are cooled, one cooling method involves delivering compressor-discharge air, or other relatively-cool fluid, to the exterior of the components. The cooling fluid may flow along the surface of the component, as in “film” cooling, or it may be guided to impinge upon the component surface. Cooling fluid may also be delivered to the interior of a component so that the component temperature may be reduced from the inside out.
Although cooling may be used to improve the high-temperature operation of blades and vanes, problems associated with this strategy limit its effectiveness in many situations. In situations where the cooling fluid is air provided by the compressor, extensive use of cooling may adversely affect engine performance by reducing the amount of air available for combustion and reducing power generating capacity of a given engine. Even in situations where cooling fluid is not provided by the compressor, it is difficult to ensure that all components are cooled sufficiently. Inadequate cooling can be troublesome, because in cases where portions of a component are not cooled sufficiently, the component may fail during operation.
While a variety of strategies have been developed to improve the high-temperature tolerance of turbine engine components, there are difficulties associated with these strategies. Additionally, as performance requirements increase, turbine components are subjected to even-more-extreme conditions. Accordingly, there remains a need in this field for strategies that allow turbine engine components to withstand extreme temperatures.